This happened to my daughter when she was a baby. Right after she turned 1, we switched her to cows milk. I was noticing that she was throwing up when she'd get the milk. Sure enough, she was lactose intolerant and she drank soymilk til she was 3. Then we tried her on cows milk again and she did fine, no problems since....she'll be 4 in a few weeks. She wasn't able to drink regular formula as a baby either, she had to drink soy.